If one examines the order of events in this Parsha, especially regarding the sin of the golden calf, one comes across an interesting argument between Rashi and the Ramban. Rashi (לשמות ל"ג:י"א בד"ה ושב) states that on the 17th day of Tammuz, the original Luchos were broken by Moshe. On the 18th day of the month, he burned the עגל, the calf, and sentenced the sinners. Then on the 19th day, Moshe went back up on to Har Sinai. The Ramban (לפסוק ז' שם), however, presents the order of events differently. He writes that on the 17th of Tammuz, Moshe broke the Luchos, burnt the עגל, and sentenced the sinners. Then on the 18th, Moshe went up again on to Har Sinai. According to the Ramban, therefore, there was actually one less day in the order of events than according to what Rashi had recorded. The question thus arises as to what made Rashi and the Ramban formulate such differing opinions.
Rav Yitzchak Zev Soloveitchik (חידושי הגרי"ז על התורה), in an attempt to answer this question, relates Rashi's opinion to the fact that if there were witnesses present and a warning issued, then any idolaters were sentenced to die by the sword, according to the Halacha governing an עיר הנדחת, a rebellious city. He thus notes that Rashi, when commenting on this episode in our Parsha, points out that Moshe sentenced the sinners among Bnai Yisrael to death by sword (שם ל"ב:כ"ז). He then explains that when a judgement of death is issued by a Jewish court, the actual carrying out of this decree is delayed one day, thereby giving the judges an extra day to try to find some way that the sentenced man can be proven innocent. (This is known as הלנת הדין.) Hence, Rashi added another day to his presentation of the order of events in accordance with this law requiring the giving of an extra day until the sentence is carried out, which he assumes must have been followed.
The Ramban, suggests Rav Soloveitchik, felt that this judgement given to Bnai Yisrael by Moshe was an exceptional kind of judgement. In other words, this judgement given by Moshe was not a formal sentencing of all these people a Jewish court, as Rashi explained. Rather, it was an emergency measure issued in that particular circumstance. Therefore, according to the Ramban, an extra day was not needed, for it was not a formal decision of a Beis Din, but an emergency measure. Rav Soloveitchik thus concludes that Rashi added a day in his order of events to allow for the extra day given to the judges to decide Bnai Yisrael's fate, in accordance with the law of הלנת הדין stated above. According to the Ramban, however, when Moshe sentenced them to death, it was an emergency measure and not a formal judicial process. Consequently, the extra day was not included in the Ramban's record of events.